1. Field of the Invention
The present invention relates to a channel-switching valve used for switching refrigerant channels depending on the operation mode in a heat-pump type air conditioner, a method of controlling such a channel-switching valve, a refrigerating cycle whose refrigerant channels are switched depending on the operation mode in a heat-pump type air conditioner, and a method of controlling such a refrigerating cycle.
2. Related Art
In an air conditioner, refrigerant channels in the refrigerant cycle are switched by a channel-switching valve when the operation mode is switched.
A typical channel-switching valve is a four-way valve, and conventional types of four-way valve include a sliding type and a rotary type.
A sliding four-way valve comprises a cylinder having a high pressure port to which a high pressure channel communicating with the outlet of the compressor is connected, a low pressure port to which a low pressure port communicating with the inlet of the compressor is connected, and two switching ports to which a switching channel communicating with an indoor heat exchanger and a switching channel communicating with an outdoor heat exchanger are connected, and a piston disposed inside the cylinder.
The piston includes a valve element which forms two connecting spaces isolated from each other inside the cylinder.
With such a sliding four-way valve, the two connecting spaces are displaced as the piston reciprocates between a first position and a second position inside the cylinder.
When the piston is in the first position, one of the two switching ports is connected to the high pressure port via one of the two connecting spaces formed by the valve element inside the cylinder, and the other one of the two switching ports is connected to the low pressure port via the other one of the two connecting spaces, thereby switching the operation mode to one of a cooling mode and a heating mode.
Meanwhile, when the piston is in the second position, the one of the switching port is connected to the low pressure port via the one of the connecting space inside the cylinder, while the other one of the switching ports is connected to the high pressure port via the other one of the connecting spaces inside the cylinder, thereby switching the operation mode to the other one of the cooling mode and the heating mode.
Whether the piston is either in the first position or in the second position in the sliding four-way valve, two pressure adjusting spaces are formed on both sides of the piston in its moving direction inside the cylinder. Each of the pressure adjusting spaces is connected to one of the two connecting spaces via a narrow equalizer channel.
One of the two pressure adjusting spaces is selectively connected to the low pressure channel via a pilot path by an open pilot valve, without going through the cylinder.
In the sliding four-way valve, the pressures in the two pressure adjusting spaces are reversed by changing the state of the pilot valve, so that the piston can be moved from the first position to the second position, or from the second position to the first position.
At this point, one of the connecting spaces is connected to the outlet of the compressor via the high pressure port and the high pressure channel, and resultantly filled with the high pressure fluid.
The other one of the connecting spaces is connected to the inlet of the compressor via the low pressure port and the low pressure channel, and thus filled with the low pressure fluid.
In order to defrost the outdoor heat exchanger in the heating mode, the four-way valve is switched so as to switch the operation mode of the refrigerating cycle from the heating mode to the defrosting mode. When switching the refrigerating cycle from the defrosting mode to the heating mode after the defrosting operation, the four-way valve is switched, because the defrosting operation is substantially the same as the cooling operation.
With the conventional sliding four-way valve described above, however, there is a problem that the power consumption is high due to energizing the coil of a solenoid which is conducted to hold a current state of the pilot valve either in the cooling (or defrosting) mode or in the heating mode in the refrigerating cycle.
When an operation mode in which the coil of the solenoid need to be continuously energized is stopped in the sliding four-way valve described above, the pilot valve is opened or closed due to the stop of the energization to the coil of the solenoid, and the four-way valve is switched even though unnecessary.
As a result, the connections of the indoor heat exchanger and the outdoor heat exchanger are switched between the high pressure channel and the low pressure channel, respectively, which causes a big noise.
As for the conventional rotary four-way valve, a typical one is disclosed in Japanese Utility Model Application Laid-Open No. 7-16084. Such a rotary four-way valve comprises a cylindrical housing accommodating a cylindrical rotor provided with plastic magnets and a valve element, a disk-like valve seat closing one end of the housing and facing the valve element, and an electromagnet at the other end of the housing.
The rotary four-way valve has a high pressure port, a low pressure port, and two switching ports on the valve seat in the circumferential direction of the housing. A high pressure channel communicating with the outlet of the compressor is connected to the high pressure port; a low pressure channel communicating with the inlet of the compressor is connected to the low pressure port; a switching channel communicating with the indoor heat exchanger is connected to one of the two switching ports; and a switching channel communicating with the outdoor heat exchanger is connected to the other one of the two switching ports.
The rotary four-way valve also has two arcuate connecting grooves formed on the end surface of the valve element facing to the valve seat. The edge of the high pressure channel communicating with the high pressure port protrudes from one of the connecting grooves, and one end of a pin penetrating the center of the valve element is disposed in the center of the valve seat.
The rotary four-way valve has plastic magnet positions magnetized so that the north pole and the south pole are alternatively situated in the circumferential direction of the housing. Two metal members facing to each other are disposed on the outer surface of the housing, and the metal members are connected to the iron core of the electromagnet.
In the rotary four-way valve of this structure, the coil of the electromagnet is energized to cause magnetic flux passing through the fixed iron core of the electromagnet and the two metal members on the outer surface of the housing. The magnetic flux corresponding to the energizing direction of the coil acts on the plastic magnets, so that the rotor rotates around the pin inside the housing between a first position in which one end of one of the connecting grooves in the circumferential direction of the housing is in contact with the edge of the high pressure channel and a second position in which the other end of the one of the connecting grooves is in contact with the edge of the high pressure channel.
When the rotor is in the first position, the high pressure port is connected to one of the switching ports via one of the connecting grooves, and the low pressure port is connected to the other one of the switching port via the other one of the connecting grooves. When the rotor is in the second position, the high pressure port is connected to the other one of the switching ports via the one of the connecting grooves, and the low pressure port is connected to the one of the switching ports via the other one of the connecting grooves.
The high pressure port communicates with the space formed between the electromagnet and the rotor inside the housing via a connecting path maintained inside the housing, so that the end surface of the rotor on the electromagnet side is subjected to a pressure equal to that of the fluid introduced into the space of the housing from the outlet of the compressor via the high pressure channel, the high pressure port, and the connecting path.
Meanwhile, the end surface of the rotor on the valve seat side is subjected to a pressure equal to that of the fluid introduced into the inlet of the compressor via the low pressure port and the low pressure channel, because the valve seat is provided with the low pressure port communicating with the inlet of the compressor via the low pressure channel.
When the compressor is in operation, the pressure acting on the end surface of the rotor on the electromagnet side becomes greater than the pressure acting on the end surface of the rotor on the side of the valve seat, and due to the pressure difference, the rotor is energized toward the valve seat.
As a result, the lower end surface of the valve element is brought into contact with and sealed to the valve seat, and the rotation position of the rotor is secured while the coil of the electromagnet is not energized.
Like the sliding four-way valve, the rotary four-way valve switches the operation mode of the refrigerating cycle between the heating mode and the defrosting mode in the same manner as in switching the operation mode between the heating mode and the cooling mode.
However, when the pressure difference becomes very large between the end surface of the rotor on the electromagnet side and the end surface of the rotor on the valve seat side, the rotor cannot rotate even if the coil of the electromagnet is energized, because the static friction caused between the lower end surface of the valve element and the valve seat due to the pushing force acting on the rotor becomes greater than the rotating force of the rotor generated by the magnetic flux acting on the plastic magnets due to the energization of the coil of the electromagnet. As a result, the rotary four-way valve becomes liable to fail to switch between the cooling (or defrosting) mode and the heating mode in the refrigerating cycle.
The switching of the rotary four-way valve is generally performed when the difference in refrigerant pressure between the outlet side and the inlet side becomes low due to a refrigerant leak from the outlet side to the inlet side inside the compressor after a certain period of time of stopping the compressor.
When switching the operation mode in the refrigerating cycle, the compressor is temporarily stopped for a certain period of time, and the switching is performed when the difference in refrigerant pressure between the outlet side and the inlet side becomes low due to a refrigerant leak from the outlet side to the inlet side inside the compressor, so that the pressure difference can be small between the both ends of the rotor, and that the static friction between the lower end surface of the valve element and the valve seat can be smaller than the rotary force of the rotor.
As a result, switching the operation mode in the refrigerating cycle is time-consuming due to the temporary stop of the compressor, and a large amount of power is required for restarting the compressor and keeping it in operation until the difference between the inlet refrigerant pressure and the outlet refrigerant pressure becomes equal to the pressure difference in the normal operation. This presents a big problem especially when switching from the heating mode to the defrosting mode for the outdoor heat exchanger.